wc -l metals.txt
grep -E '中国|中国香港|中国台北' metals.txt | sort -k2,2nr -k3,3nr -k4,4nr
sort -t'', -k4nr metals.txt | head -n5 | cut -d'', -f1
sort -k4,4nr metals.txt | head -n 5 | awk -F',' '{print $1}'
sort -t',' -k2,2nr metals.txt | head -n 5 | awk -F',' '{sum+=$2} END {print sum}'
